Coating composition



Patented May 18, 1943 UNITED STATES PATENT OFFICE roughs, Plttsbnrgvania Industrial notation of Pennsy Pa assignora to PennsylemlcalCorporation, a corlvania No Drawing. Application July 16, 1940, SerialNo. 345,860

Claims.

This invention relates to a thermoplastic coating composition purposedparticularly as a coating for paper and other fibrous or cellulosic materials, such as cloth of different sorts.

Heretofore the substances preponderantly used for coating paper havebeen paraffin wax and coating compositions containing paraflin wax andone or more of the more expensive types of resin, such as coatingcompositions containing vinyl resins or the polymers of acrylic acidesters.

Parafiin wax is the typical paper coating material, but of itself doesnot give to a maximum all the desired qualities of a paper coating, inthat it tends to opacity is of relatively low-melting point and has lowresistance to abrasion. It also has poor heat-sealing properties. Paramnwax being a mixture of the higher series of allphatic hydrocarbons hasvery poor compatibility with many other substances which "would tend tomodify its qualities for the better, since it is an even poorer solventfor most resins, and the like potential modifying substances than arethe evaporative aliphatic hydrocarbon solvents of relatively low solventpower. It is possible by hydrogenation to make certain resins,inherently incompatible with paraflin, compatible with it.

We have discovered that the resins produced by polymerization ofselected unsaturated carbocyclic terpadienes are, without hydrogenationor other treatment, highly. compatible with paraffin wax to such extentthat they blend in all proportions with the wax without granulation inthe mixture or separation between the wax and resin. Thus, we havediscovered that we are able successfully to blend with paraffin wax thehighest melting terpene resins which may be made by polymerizingselected unsaturated constituents of gum spirits of turpentine and otherterpene starting materials; such as those high polymers of beta-pinene,and terpene mixtures in which beta-pinene preponderates, which are'disclosed in the application of Samuel G. Burroughs, Serial No. 288,390filed August 4. 1939. We have found that by so doing, we are able toproduce with paraflin wax a homogeneous mixture having a. melting pointmuch higher than that of the paraifin wax, and yet which possesses waxcharacteristics. Such a blend of terpene resin and parailln waxes, inaccordance with the proportional inclusion of the resin and ,its meltingpoint, has a greater resistance to abrasion than parailln wax, and hasbetter heat-sealing properties than the wax taken by itself. If aterpene resin mixed with the wax is oi. sufficiently high melting pointand is included in the composition in sufllciently great proportion, wehave also discovered that paper coated with the mixture is translucentand in practical eflect transparent, and that it possesses a glossyfinish. so that the coated paper is suitable for use in display packagesior foods and other materials.

The proportions in which terpene resins, even those of the highestmelting point which have been made, are compatible with paraifin wax areunlimited, so that there may be included in the wax mixture any relativeproportions which are desirable or economical in making a compositionfor use in making any specialized type of coated paper or fabric. Inthis connection it should be emphasized that the terpene resins requireno addition or modification in order that they may possess such broadmeasure of compatibility with the parafiin wax.

In line with the foregoing, we may make a paper-coating compositioncontaining, for example, paraflln wax, and 10% of high-melting terpeneresin. Such composition has good heatsealing properties, in which theparaflln wax is of itself deficient, and has a higher gloss and lesseropacity than paramn wax. We have found that even this relatively smallproportional inclusion of terpene resin, and this is particularly trueif the resin has a high melting point such as a melting point of from250 F. upward, gives a coating composition which, when applied, hasbetter film continuity and better resistance to abrasion than unmodifiedparaflln wax.

As exemplary of coating compositions capable of rendering papertransparent and giving it a glossy finish, so that it is well suited forthe packaging of foods and the like, we may mix paraflln wax andhigh-melting terpene resin, such as a terpene resin melting about 275F., in a proportion of from 30% and more of the resin.

A coating composition in which the brittleness of the resin is modifiedby an addition of wax may be made by mixing the resin with 25% or evenless of paraflln wax. Such composition is useful for glazing paper forpurposes in which great transparency or translucency is of primaryimportance.

In all mixtures of the wax and resin the dualities imparted to themixture by the resin are more striking for any proportional inclusion ofthe resin, the higher the melting point of the resin which is included.

In addition to paraflin wax, all the other waxlike materials. whether orno they be wholly hydrocarbon in nature, are compatible with terpeneresin oi all melting points. Thus, for example, in

our thermoplastic coating composition we have made homogeneous mixturesof terpene resin having melting points up to the highest currentlyobtainable with ceresin wax, candelilla wax, carnauba wax, montan wax,Japan wax; and synthetic waxes, such as those produced by theesterification of long chain alcohol with fatty acids, and hydrogenatedfats and oils. Most 01' the other wax-like material lack the chemicalresistance oi paraflin wax, but otherwise have properties making themuseful in a thermoplastic coating composition of the sort with which weare concerned.

Among the wax-like materials which we may use, paramn wax may beconsidered the preferred waxy ingredient, both for reasons oi economy.and because its other properties, such as light color, chemicalresistance, and relatively high melting point render it suitable. It isthe wax typically used for paper coating, and in known thermoplasticcoating compositions for paper coating and like uses. The usual highgrade oi paraflln wax obtained from petroleum oils melts at about 140 F.Certain other wax-like materials, typically carnauba wax, melt atrelatively high temperatures.

In our coating composition it is important that the terpene resin behigher melting than the waxlike material with which it is mixed, inorder that the more substantial advantages coming from its inclusion maybe had. This is true with whatever one, or more of the wax-likematerials it may be mixed. It follows that, in order to obtaincompositions having properties best suited to particular materials to becoated, and particular uses to which the materials thus coated are to beput, we vary the melting point of the terpene resin and its proportionalinclusion in accordance with the melting temperature of the wax-likematerial for any intended use of the composition. It is roughly truethat inclusion of the terpene resin in any proportion with a waxlikematerial proportionally modifies the properties of that material, andinclusion of a wax-like material in any proportion with a. terpeneresin. proportionally modifies the properties of the r sin.

Because of the compatibility of the highest melting terpene resin withall wax-like materials, and because there is nothing critical about theproportional inclusion of the ingredients of the composition, it is asimple matter to apportion the ingredients oi the composition inaccordance with their melting properties and the intended use or thecomposition. Thus. we may give, as roughly illustrative, a coatingcomposition for a coated paper of good heat-sealing propertiesconsisting essentially of about 90% paraflln wax melting at about 140 F.and-about 10% of terpene resin melting at about 300 F. As a compositionfor glazed paper for use in display package and the like, we may give asroughly exemplary a composition consisting essentially of about 40%paraffln wax melting at about 140 F. and about 60% ot terpene resinmelting at about 250 F. For a composition having primarily theproperties of a plasticized resin, we may give as roughly exemplary oneconsisting essentially of about 25% paraflin wax melting at about 140'F. and about 75% oi! terpene resin melting at about 275' F. It is asimple matter to obtain varied desired properties of the coatingcomposition by varying the proportions oi the ingredients and byselecting the ingredients on the basis oi their melting temperatures. Byreference to the melting temperatures of all the various other wax-likematerials. it is also a simple matter to make up from the other wax-likematerials and terpene resin coating compositions which parallel theparaflln-wax compositions in the properties dependent upon th meltingcharacteristics or the ingredients.

All variants oi the terpene-containing coating composition abovedescribed are thermoplastic compositions, and by this we mean that inapplying them they are caused to flow by heat. They thus may be preparedfor application, and may be applied by any procedure known to besuitable for the application of coatings oi paraflln-wax and otherwax-like materials, or coating compositions consisting essentially ofsuch materials and ingredients other than terpene resins. The mixture ofthe ingredients is made by fusing them together, and may be appliedeither as made or by refusing the mixture. In either case the meltingtemperature of the resin is lowered by its intimate association with thewax-like material, or materials with which it is mixed. It may beapplied to paper or fabric in any of the well-known methods by whichthey have been coated; as by immersion. hot-spraying, use of the doctorknife, or working in hot rolls. It may be applied to the surfaces ofmore substantial bodies, in any way known to be suitable ior applyingthermoplastic coatings; as by immersion or hot-spraying.

Our coating composition, consisting essentially of an unaltered andrelatively inexpensive terpene resin and a wax-like material, which maybe the relatively inexpensive parafiln wax, thus has commercialadvantage over coating compositions of similar sort which include withthe wax modifying ingredients of some more expensive type. It has, incomparison with the wax alone, greater resistance to abrasion, betterheat-sealing properties due to the interent tendency of the resin to actas a thermoplastic adhesive, gloss and transparency in higher order, andthe ability to improve the capacity of paper coated with it to receive asuitable printing ink without blurring or spreading.

Other advantageous qualities of our coating composition are attributableto the wholly hydrocarbon nature of its terpene resin content. Forexample, that resin tends to impart to the coating composition its owninherent qualities of chemical resistance to acids, alkalis, salts, andother reagents. It also tends to impart to the coating composition inwhich it is included resistance to enzyme reactions, and thus to renderpaper or fabric coated with it suitable for use in packaging foods. It,as is usual, we include the terpene resin with paramn wax, which is alsowholly hydrocarbon in nature, the coating composition possesses thosequalities in maximum order.

To our base coating composition, consisting essentially of a wax-likematerial and a highermelting terpene resin, other ingredients forimparting specific additional qualities may be added. Thus, a number ofhigh molecular weight strength-increasing substances are compatible bothwith the paraflin wax, or other wax-like material, and with the terpeneresin. For example, we may add to the composition a minor proportion ofstrength-increasing substances. such as the polymers of isobutylene, thelower polymerized forms of the higher esters of acrylic acid, such asbutyl-methacrylate, worked rubber, the resin content oi rubber, andrubber derivatives exemplified by chlorinated rubber: making suchaddition to the essential composition when highly elastic coatings aredesired.

Additions, such as those above noted, may be made to our essentialcomposition without departure from our invention, and while remainingwithin the definition of that invention as contained in our appendedclaims.

We claim as our invention:

1. The herein-disclosed thermoplastic coating composition consistingessentially of a homogeneous mixture of paramn wax and thermoplasticresin melting higher than the parailin wax and composed of polymers ofunsaturated carbocyclic terpadienes.

2. The herein disclosed thermoplastic coating composition having as itsmajor component a homogeneous mixture of a wax and thermoplastic resinmelting higher than the wax and composed ot polymers of unsaturatedcarbocyclic terpadienes in the approximate proportion of 10% to 75% ofthe terpene polymers and 25% to 90% of the wax.

3. The herein disclosed thermoplastic coating composition consisting ofa homogeneous mixture of paraffin wax and thermoplastic resin meltinghigher than the paraflin wax and composed oi polymers of unsaturatedcarbocyclic terpadienes in the approximate proportion of 10% to 75% ofthe terpene polymers and 25% to 90% of the wax.

4. The herein-disclosed thermoplastic coating composition consistingessentially of a homogeneous mixture of a wax and thermoplastic resinmelting higher than the wax and composed of polymers of unsaturatedcarbocycllc terpadienes.

5. The herein-disclosed thermoplastic coating composition having as itsmajor component a homogeneous mixture of a wax and thermoplastic resinmelting higher than the wax and composed oi' polymers of unsaturatedcarbocyclic terpadienes.

FRANK W. CORKERY. SAMUEL G. BURROUGHS.

